This invention relates to direct current (DC) voltage regulation and an initial surge of current, typically with an associated drop in voltage, at the input of the voltage regulator upon the voltage regulator being turned from OFF to ON. The magnitude of such a current surge and associated voltage drop is greater when multiple voltage regulators are connected in parallel to the same power source and are switched from OFF to ON at substantially the same time.
Many circuits benefit from having a regulated DC supply voltage. In order to enhance output voltage stability, voltage regulator circuits often utilize a capacitor connected at the regulated output voltage terminal to ground that functions as a low pass filter to inhibit rapid voltage fluctuations at the regulated output voltage. While this is beneficial, as this output capacitor is normally in a discharged state, i.e. zero voltage across the capacitor, when the voltage regulator circuit is OFF. Depending on the resistance in series with the capacitor, large currents can initially flow upon turn-ON of the voltage regulator until the output capacitor becomes charged. Even if such a capacitor is not utilized as part of the voltage regulator circuit, the load circuit that receives the regulated voltage output from the voltage regulator circuit may have an input capacitor or equivalent capacitance that can give rise to such a current surge. As the magnitude of an initial current surge approaches the maximum current that can be delivered by the voltage source that supplies the voltage regulator, the voltage at the supply voltage source (input to the voltage regulator) will drop. If it drops to a voltage level approaching the target regulated voltage output of one of the voltage regulators being supplied by the voltage source, then the output voltage of that voltage regulator will fall below the target voltage during such a current spike. This is undesirable and may cause errors or malfunctions by the load circuitry fed from the voltage regulator.
FIG. 1 shows an embodiment 100 of voltage supply system with a plurality of voltage regulators 105 connected in parallel to an unregulated voltage source 110, e.g. a battery, etc. Each of the voltage regulators 105 are connected to a corresponding load circuit 115. The voltage regulators 105 have a control terminal 120 by which the voltage regulators 105 are turned OFF and ON by a control voltage. If it is possible to sequence to the turning ON the respective voltage regulators 105, then any concurrent current surge and associated voltage drop induced at the unregulated voltage source can be minimized. However, the demands of the load circuits 115 may make such sequencing undesirable. Additionally, if the surge current from turning one of the voltage regulators 105 from OFF to ON is sufficient to cause the voltage being supplied by the unregulated voltage source to fall below the target voltage output of one of the other voltage regulators 105, then sequencing of the turn ON of the voltage regulators 105 will not eliminate this problem. There exists a need for an improved way to minimize, if not eliminate, such undesired voltage drops at the unregulated voltage source due to turn ON current surge by a voltage regulator.